Generally the embodiments of the present invention relate to so-called correction tape dispensers or correction devices which are adapted to apply a correction tape on a substrate.
The use of a frictional clutch in a correction device is known in the prior art. The frictional clutch serves for creating drive adjustment for a take-up reel of the correction device for transferring a film from a backing tape onto a substrate, whereby the take-up reel is being driven such that the backing tape portion being supplied to the take-up reel is always slightly tensioned. The frictional clutch should ensure that a predetermined tension is not exceeded so that the backing tape is not disrupted.
An example for such a frictional clutch comprises a supply reel for feeding a coating film transfer tape and a take-up reel for recovery of the used coating film transfer tape which are both rotatably mounted in a casing. The supply reel includes a supply cylinder and a drive gear wheel having a boss. An O-ring serving as a friction member is provided on an outer periphery of the boss of the drive gear wheel whereby the supply cylinder is mounted on the outer periphery of and in friction contact with the O-ring, thus sandwiching and compressing the O-ring in between the boss and the supply cylinder.
However, these frictional clutch systems know in the prior art have the disadvantage that due to tolerances of the components, namely the boss of the drive gear wheel and/or the supply reel cylinder, of only a few tenths of a millimeter, these deviations have a great influence on the resulting frictional force. That means that a few tenths of a millimeter percentally result in a high variation considering the typical diameter of an O-ring of only a few millimeters. If now, the drive gear wheel boss is a few tenths of millimeters too large and/or the supply reel cylinder is only a few tenths of a millimeter too small, a very high frictional force results, rendering the clutch too hard and, thus, rupture of the backing tape has to be encountered.
Therefore, an embodiment of the present invention is based on the object to provide a frictional clutch, a driving mechanism employing the frictional clutch and a corresponding correction device, in which the frictional force of the frictional clutch is less dependent on manufacturing tolerances.
This object is solved by a frictional clutch having the features of a frictional clutch for a correction device that includes a rotatable supply reel with a circular center opening and a rotatable take-up reel being arranged laterally spaced apart from the supply reel, the take-up reel having an outer circumferential surface onto which a correction tape is to be wound up and the supply reel having an outer circumferential surface from which the correction tape is to be wound off, wherein the outer circumferential surface of at least one of supply reel and take-up reel is provided with a groove in which an elastic tensioning element is accommodated, the radial circumferential groove being at its bottom at least partially opened such that the elastic tensioning element is biased into the center opening, a driving mechanism having the features of that include a drive gear wheel (i) in the center of which a cylindrical boss is provided on which the supply wheel is arranged with circular center opening, and a driven gear wheel, on which a take-up reel is arranged, whereby the drive gear wheel (ii) engages the driven gear wheel, and a correction device having the features of a casing having an upper body and a lower body, the casing being provided with a tip opening, through which a tip for applying a correction tape onto a surface of a substrate extends; a drive gear wheel (i) in the center of which a cylindrical boss (i) is provided on which a supply reel is arranged having a center opening and a circumferential surface from which the correction tape is to be wound off; a driven gear wheel which engages the drive gear wheel (ii) and on which a take-up reel is arranged having a circumferential surface on which the correction tape is to be wound up wherein the outer circumferential surface of the supply reel is provided with a circumferential radial groove in which an elastic tensioning element is accommodated, the circumferential radial groove being at its bottom transected at least partially such that the elastic tensioning element projects into the center opening secantically, when it is in a stress-relieved condition.
According to an embodiment of the present invention, a frictional clutch for a correction device is provided that includes a rotatable supply reel with a circular center opening and a rotatable take-up reel being arranged laterally spaced apart from the supply reel, the take-up wheel having an outer circumferential surface onto which a correction tape is to be wound up and the supply reel having an outer circumferential surface from which the correction tape is to be wound off, wherein the outer circumferential surface of the supply reel is provided with a radial circumferential groove in which an elastic tensioning element is accommodated, the radial circumferential groove being at its bottom at least partially transected such that the elastic tensioning element projects into the center opening secantically, when it is in a stress-relieved condition. When the frictional clutch is employed, i.e., when mounted on a driving mechanism of a correction device, the elastic tensioning element smoothly adapts the circular shape of the supply reel or the boss, respectively, onto which the supply reel is mounted, to thus contact the circumferential surface of the boss and apply a well-defined frictional force.
According to this construction, the compression exerted on the O-ring employed in a frictional clutch known in the prior art is replaced by the circumferential expansion of the elastic tensioning element. This has the advantage that tolerances of only a few tenths of a millimeter now are minor or negligible, compared to the length of the elastic tensioning element of, e.g., three to five centimeters. These variations have only very little influence on the resulting frictional force.
Moreover, the elastic tensioning element can be preassembled on the supply reel from the outside, such that the tensioning element and the supply reel can be mounted on the supply reel boss in only one working cycle, facilitating the production of the correction tape, and, thus, reducing production costs.
The frictional clutch of an embodiment of the present invention is particularly adapted for a torque-restricting power transmission between a reel and a rotating element of a correction device for applying a film of a backing tape onto a substrate. This frictional clutch, however, can either be assigned to a supply reel or a take-up reel of the correction device.
The embodiments of the present invention and further advantages, which can be achieved by the embodiments of the present invention, will now be explained in detail by means of a preferred embodiment with reference to the drawings in which
FIG. 1 shows a sectional side view of a correction device 1 according to prior art which can be used to erase characters of the like on a substrate.